Stabilized pharmaceutical composition

ABSTRACT

A pharmaceutical formulation of taxol and polyethoxylated castor oil is disclosed to be relatively acidified to pH of less 8.1 and preferably within a pH range of 5 to 7, inclusively, by an acidifying agent. Ethanol is optionally included in the formulation which is adapted for use in a body for the treatment cancer. A formulation method is disclosed and includes the step of mixing an acid with a carrier material, such as polyethoxylated castor oil, to form a carrier solution after which taxol is added in an amount such that the resulting pH is less than 8.1 and preferably in a pH range of 5 to 7. Ethanol may optionally be slurried with the taxol before mixing with the carrier solution. A variety of acidifying agents, a preferred one being anhydrous citric acid, are described.

This a division, of application Ser. No. 08/594,478, filed Jan. 31, 1996, U.S. Pat. No. 5,733,888.

BACKGROUND OF THE INVENTION

Taxol is a compound extracted from the bark of a western yew, Taxus brevifolia and known for its antineoplastic activity. It is described for example in The Merck Index, Eleventh Edition 1989, monograph 9049.

In 1977, taxol was chosen for development as an antineopiastic agent because of its unique mechanism of action and good cytotoxic activity against IP implanted D16 melanoma and the human X-1 mammary tumor xenograft. Taxol is believed to function as a mitotic spindle poison and as a potent inhibitor of cell replication in vitro. Other mitotic spindle points (colchicine and podophyllotoxin) inhibit microtubule assembly. Taxol employs a different mechanism of action since it appears to shift the equilibrium of polymerimization/depolymerization toward polymer assembly and to stabilize microtubules against depolymerization under conditions which would cause rapid disaggregation of microtubules. The interference with the polymerization/depolymerization cycle in cells appears to interfere with both the replication and migration of cells.

After extensive preclinical screening in mouse tumor models, taxol entered clinical trials in 1983. Over the past few years, taxol has demonstrated good response rates in treating both ovarian and breast cancer patients who were not benefiting from vinca alkaloid or cisplatin therapy. It has also shown encouraging results in patients with other types of cancer including lung, melanoma, lymphoma, head and neck.

For further information, reference may be made to the U.S. National Cancer Institute's Clinical Brochure for Taxol, revised July 1991, and papers presented at the Second National Cancer Institute Workshop on Taxol and Taxus held in Alexandria, Va. USA on Sep. 23-24, 1992.

BRIEF DESCRIPTION OF THE INVENTION

It is a disadvantage of the known formulation that the taxol therein degrades, with the result that the shelf life of the formulation is unsatisfactory, and there is therefore a need for a taxol solution of improved stability.

Accordingly, in a general aspect the invention provides a solution containing taxol, cremophor EL™ and ethanol, characterized in that the pH of the solution has been adjusted into the range 1 to 8 by addition of an acid.

Acids in the form of powders, for example citric acid, are preferred over those which contain water, for example sulfuric acid. The most preferred acid for use in accordance with the present invention is citric acid but a wide range of acids may be used including the following:

Citric acid--monohydrous

Citric acid--anhydrous

Citric acid--hydrous

Acetic acid

Formic acid

Ascorbic acid

Aspartic acid

Benzene sulplonic acid

Benzoic acid

Hydrochloric acid

Sulphuric acid

Phosphoric acid

Nitric acid

Tartaric acid

Diatrizoic acid

Glutamic acid

Lactic acid

Maleic acid

Succinic acid

DETAILED DESCRIPTION OF THE INVENTION

Due to its limited solubility in water, Taxol is usually prepared and administered in a vehicle containing cremophor EL™ (a polyethoxylated castor oil which acts as a solubilizer) and ethanol. A commercially available solution supplied by Bristol-Myers Squibb (BMS) is formulated with these components and has a pH of 9.1.

As indicated above, the invention essentially teaches addition of an acid to a taxol formulation to adjust its pH into the range 1 to 8, preferable 5 to 7.

In a preferred procedure adopted by the applicant, which it will be clearly understood is non-limiting, the following steps were carried out:

Mixing Instructions

Solution 1

Citric acid was dissolved in absolute alcohol, using a ratio of 8 mls of absolute alcohol to 1 gram of citric acid, and the solution was stirred for fifteen (15) minutes.

Solution 2

Cremophor EL was weighed out into the main mixing vessel.

Solution 3

Solution 1 was added to solution 2, and the container used for solution 2 was washed with a minimum quantity of absolute alcohol to ensure complete transfer of the citric acid. Solution 3 was mixed and bubbled with nitrogen for at least 15 minutes. The taxol was weighed out and slurried using absolute alcohol, using a ratio of 8 ml of absolute alcohol to 1 gm of taxol. The slurried taxol was added to solution 3 and the slurrying vessel was washed with a minimum quantity of absolute alcohol. Solution 3 was adjusted to 75% of required volume using absolute alcohol, and thoroughly stirred for at least 45 minutes until completely dissolved. Once completely dissolved, the volume was checked and made up as necessary with absolute alcohol and the final solution stirred for 5 minutes.

EXAMPLE 1

A solution was prepared with the following formulation:

    ______________________________________                                         Formulation: (Sample 1)                                                        ______________________________________                                         Cremophor EL       0.5 mL                                                        Citric Acid (Anhydrous) 2.0 mg                                                 Taxol 6.0 mg                                                                   Absolute Alcohol to 1.0 mL                                                   ______________________________________                                    

The pH of this solution was determined as 6.1.

The stability of this sample was compared with a sample prepared by the formulation stated in the NCI Taxol Clinical brochure (as follows) which had a pH of 9.1.(Sample 2)

    ______________________________________                                                Sample 2        per mL                                                  ______________________________________                                                Taxol           6 mg                                                      Cremophor EL 0.5 mL                                                            Absolute Alcohol to 1 mL                                                     ______________________________________                                    

The solutions were filled into clear type 1 glass 5 mL vials and sealed with rubber bungs.

The solutions were stored at 40° C. for 7 (seven) days and the stability results are shown in Table 1.

    ______________________________________                                                        Sample 1                                                                              Sample 2                                                 ______________________________________                                         pH               6.2      9.0                                                    Potency 96.6 86.7                                                              Major individual 0.3% 5.1%                                                     impurity                                                                       Total impurities 2.0% 12.2%                                                  ______________________________________                                    

Clearly Sample 1 showed significantly increased stability over Sample 2.

EXAMPLE 2

A solution was prepared with the following formulation:

    ______________________________________                                         Formulation: (Sample 3)                                                        ______________________________________                                         Cremophor EL       0.5 mL                                                        Taxol 6.0 mg                                                                   Absolute Ethanol to 1 mL                                                     pH adjusted to 6.6 with 1.0 M Acetic Acid.                                     ______________________________________                                    

The solution was filled into clear type I glass 5 mL vials and sealed with rubber bungs.

The solution was stored at 40° C. for 7 days.

The stability results obtained are compared to those seen with Sample 2.

    ______________________________________                                                        Sample 3                                                                              Sample 2                                                 ______________________________________                                         pH               6.7      9.0                                                    Potency 97.5 86.7                                                              Major individual 0.3% 5.1%                                                     impurity                                                                       Total impurities 2.3% 12.2%                                                  ______________________________________                                    

Again the significantly superior stability of the formulation according to the invention (Sample 3) is evident.

It will be clearly understood that the invention in its general aspects is not limited to the specific details referred to hereinabove. 

We claim:
 1. A method of formulating a taxol solution for injection in which the taxol does not readily degrade, comprising the following steps:mixing acid with a carrier material to form a first carrier solution; and mixing taxol with the first carrier solution to form a taxol solution having a pH of less than 8.1 whereby the taxol in the taxol solution does not readily degrade.
 2. An improved pharmaceutical carrier composition useful for combining with taxol to yield a taxol formulation, the improvement comprising mixing an acid with said carrier composition.
 3. The improved pharmaceutical carrier composition of claim 2, wherein said carrier composition comprises polyethoxylated castor oil.
 4. The improved pharmaceutical carrier composition of claim 3, wherein said carrier composition further comprises ethanol.
 5. The improved pharmaceutical carrier composition of claim 2, wherein said acid is a mineral acid.
 6. The improved pharmaceutical carrier composition of claim 2, wherein said acid is an organic acid.
 7. The improved pharmaceutical carrier composition of claim 6, wherein said organic acid is citric acid.
 8. The improved pharmaceutical carrier composition of claim 7, wherein said citric acid is anhydrous.
 9. The improved pharmaceutical carrier composition of claim 6, wherein said organic acid is acetic acid.
 10. The improved pharmaceutical carrier composition of claim 2, having a resulting pH of less than about
 7. 11. The improved pharmaceutical carrier composition of claim 10, having a resulting pH of from about 7 to about
 5. 12. The improved pharmaceutical carrier composition of claim 3, wherein said acid is a mineral acid.
 13. The improved pharmaceutical carrier composition of claim 3, wherein said acid is an organic acid.
 14. The improved pharmaceutical carrier composition of claim 13, wherein said organic acid is citric acid.
 15. The improved pharmaceutical carrier composition of claim 14, wherein said citric acid is anhydrous.
 16. The improved pharmaceutical carrier composition of claim 13, wherein said organic acid is acetic acid.
 17. The improved pharmaceutical carrier composition of claim 3, having a resulting pH of less than about
 7. 18. The improved pharmaceutical carrier composition of claim 17, having a resulting pH of from about 7 to about
 5. 19. The improved pharmaceutical carrier composition of claim 4, wherein said acid is a mineral acid.
 20. The improved pharmaceutical carrier composition of claim 4, wherein said acid is an organic acid.
 21. The improved pharmaceutical carrier composition of claim 20, wherein said organic acid is citric acid.
 22. The improved pharmaceutical carrier composition of claim 21, wherein said citric acid is anhydrous.
 23. The improved pharmaceutical carrier composition of claim 20, wherein said organic acid is acetic acid.
 24. The improved pharmaceutical carrier composition of claim 4, having a resulting pH of less than about
 7. 25. The improved pharmaceutical carrier composition of claim 24, having a resulting pH of from about 7 to about
 5. 26. A pharmaceutical taxol composition comprising taxol and a pharmaceutically-acceptable carrier wherein said pharmaceutical taxol composition has a pH less than or equal to 7.0.
 27. The pharmaceutical taxol composition of claim 26 having a pH between 5 and
 7. 28. The pharmaceutical taxol composition of claim 26 further comprising ethanol as a constituent thereof.
 29. The pharmaceutical taxol composition of claim 28 having a pH of between 5 and
 7. 30. The pharmaceutical taxol composition of claim 26, wherein said pharmaceutically-acceptable carrier is polyethoxylated castor oil.
 31. The pharmaceutical taxol composition of claim 26, wherein said composition is anhydrous.
 32. An improved method of formulating a pharmaceutical taxol solution, such that the taxol does not readily degrade, comprising the following steps:mixing taxol with a carrier material to form a taxol solution; and reducing the pH of said taxol solution to a level whereby the taxol solution is stabilized such that at least 95% of the taxol potency is retained when the composition is stored at 40° C. for seven (7) days.
 33. The method of claim 32, wherein said carrier material is polyethoxylated castor oil.
 34. The method of claim 32 further comprising the step of slurrying said taxol in alcohol before mixing said taxol with the carrier material.
 35. An article of manufacture comprising a container and a pharmaceutical formulation contained therein, said pharmaceutical formulation comprising a pharmaceutically-acceptable carrier and taxol, wherein said pharmaceutical formulation has a pH of about 7 or less.
 36. The article of claim 35, wherein said pharmaceutical-acceptable carrier is polyethoxylated castor oil.
 37. The article of manufacture of claim 35, wherein said pharmaceutical formulation further comprises ethanol.
 38. The article of manufacture of claim 35, wherein said pharmaceutical formulation has a pH between 5 and
 7. 39. The article of manufacture of claim 35 further comprising instructions for administering said pharmaceutical formulation to a patient.
 40. A pharmaceutical taxol composition comprising:taxol; polyethoxylated castor oil; and ethanol, wherein said taxol composition has a pH sufficient to improve the stability of said taxol such that at least 95% of the taxol potency is retained when the composition is stored at 40° C. for seven (7) days.
 41. A pharmaceutical taxol composition comprising:taxol; polyethoxylated castor oil; and an acid in sufficient amounts to improve the stability of the taxol such that at least 95% of the taxol potency is retained when the composition is stored at 40° C. for 7 days.
 42. The pharmaceutical taxol composition of claim 41, wherein said acid is an organic acid.
 43. The pharmaceutical taxol composition of claim 41, wherein said acid is a mineral acid.
 44. The pharmaceutical taxol composition of claim 41, wherein said acid is citric acid.
 45. The pharmaceutical taxol composition of claim 44, wherein said citric acid is monohydrous.
 46. The pharmaceutical taxol composition of claim 44, wherein the citric acid is hydrous.
 47. The pharmaceutical taxol composition of claim 41, wherein said acid is formic acid.
 48. The pharmaceutical taxol composition of claim 41, wherein said acid is ascorbic acid.
 49. The pharmaceutical taxol composition of claim 41, wherein said acid is aspartic acid.
 50. The pharmaceutical taxol composition of claim 41, wherein said acid is benzene sulphonic acid.
 51. The pharmaceutical taxol composition of claim 41, wherein said acid is benzoic acid.
 52. The pharmaceutical taxol composition of claim 41, wherein said acid is hydrochloric acid.
 53. The pharmaceutical taxol composition of claim 41, wherein said acid is sulphuric acid.
 54. The pharmaceutical taxol composition of claim 41, wherein said acid is phosphoric acid.
 55. The pharmaceutical taxol composition of claim 41, wherein said acid is nitric acid.
 56. The pharmaceutical taxol composition of claim 41, wherein said acid is tartaric acid.
 57. The pharmaceutical taxol composition of claim 41, wherein said acid is diatrizoic acid.
 58. The pharmaceutical taxol composition of claim 41, wherein said acid is glutamic acid.
 59. The pharmaceutical taxol composition of claim 41, wherein said acid is lactic acid.
 60. The pharmaceutical taxol composition of claim 41, wherein said acid is maleic acid.
 61. The pharmaceutical taxol composition of claim 41, wherein said acid is succinic acid. 